Air treating devices in which an operative fluid is evaporated to effect the air treatment have been in use for many years. One such device is disclosed in U.S. Pat. No. 3,587,968, which issued to C. Hennart et al. on June 28, 1971. In this patent a sealed reservoir houses the liquid to be evaporated. A destructible closure device interrupts communication between the interior of a wick tube and the atmosphere before use. To activate the device, means is provided to destroy the closure device.
One of the problems associated with such devices is that the consumer usually does not know when the operative fluid has been exhausted. Consequently, such devices are frequently maintained in use even though they are no longer effective and the consumer does not have the air treatment desired until the exhausted condition of the device is finally realized and the device is replaced with an operative substitute. The present invention provides a means for readily detecting visually that the operative fluid has been exhausted.
The use of run-out signal indicators is not new. Means for indicating exhaustion of a primary or operative fluid or material have been employed in a number of inventions. For example, U.S. Pat. Nos. 1,337,029 and 1,337,030, issued to P. R. Weitzel on Apr. 13, 1920 disclose a soap dispenser that employed two discrete layers of soap, one of which was intended to be expressed from the container last and to have a distinguishing characteristic, such as scent or color, to signal that the supply of soap is almost exhausted.
U.S. Pat. No. 2,636,644, issued to A. Taylor on Apr. 28, 1953, teaches the use of materials of different viscosity such that a high viscosity material, which is situated at the bottom of a collapsible tube in small quantity, causes a sudden increase in the force required to express the contents after the primary, or low viscosity material, is exhausted. A. Herring et al., U.S. Pat. No. 2,671,424, issued Mar. 9, 1954, relates to a pressurized dispenser in which the fluid pressure drop that occurs as the primary fluid is used, breaks a smaller, dye-bearing receptacle to indicate fluid depletion.
Knapp et al., U.S. Pat. No. 4,051,628, issued Oct. 4, 1977, discloses a container to dispense a hydrophilic gel into a growing medium. The gel contains a soluble dye that diffuses through the growing medium at a faster rate than the gel so that the growing medium changes (loses) color when the gel is nearly exhausted.
In Munden, U.S. Pat. No. 4,128,508, issued Dec. 5, 1978, a color change signal system is shown. The device employs two miscible fluids, one being a perfume and the other being either an acid or a base, and a substrate capable of transporting the fluids. The substrate is impregnated with a pH sensitive dye so that the acid or base, selected to volatize at a rate equal to that of the perfume, would, when depleted, cause a color change in the substrate thereby indicating depletion of the perfume. Assuming that the device will perform satisfactorily, it will be seen that there will be many constraints in the system design imposed by the miscibility, evaporation and pH properties of the fluids used.
It is an object of the present invention to provide an air treating device employing a color change system to signal exhaustion of the operative fluid, which system has different constraints than these systems presently known, in order to provide greater flexibility in the design and performance of such devices.
Another object of this invention is to provide an air treating device that is attractive in use, effective in performance, easy to operate and provides a visual signal based on highly controllable physical properties to connote exhaustion of the operative fluid.